Two-way television system



April 1940- A. MCL. NICOLSON 2,l 9 7 ,005

TWO WAY TELEVISION SYSTEM Filed May '7, 1928 5 Sheets-Sheet 1 Fig.1 la, 1 v 3 J L q 2 5 r I) I 7 l6 2 l I 2 7 Q f ,8 g 9 v20 H 110 2 I2| 1 I '3 I2 24 23 '4 I5 LJ v 5 Fl 2 2& l4 lib 9 3 /U 1 PHOTO I I Z??? 29 451.1. I 28 FILTER \l5 2F FILTER O INVENTOR Q ALEXANDER M LEAN NICOLSON ATTOiQNEY April 16, 1940.

A. MOL. NICOLSQN TWO WAY TELEVISION SYSTEM Filed May 7, 1928 Sheets-Sheet 2 AMP. FILTER AMP.

DRIVING MOTOR FOR SCANNER R. an T- s. P.

69 PHOTO 8 ELECTRIC AMP CELL PHASE AND INTENSITY CONTROLLER 73/ MOD 74/ OSCILLATOR g INVENTOR ALEXANDER MLEAN NICOLSON April 16, 1940.

A. M L. NICOLSON 2,1 7,005

TWO my TELEVISION SYSTEM Y Filed May 7, 1928 5 Sheets-Sheet 4 MODULATO AND OSCILLATOR SCANNER U55 F1 10 AMP. I /ll 5 I58 5 AMP. CONVERTER 8a 2 I56 I I57 59 I ISBa,

? TO LIGHT l6l.

CONTROL O R C i g FILTER I52 '53 7 INVENTOR ALEXANDER MLEAN NICOLSON ATTORN EY April 16, 1940. A, McL. NICOLSON 2,197,005

TWO WAY TELEVISION SYSTEM Filed May 7, 1928 5 Sheets- Sheet 5 Fig. 12 II/ RECEIVER AND FILTER LOCAL 5IGNAL GENERATOR JIHH RETARD- ING 3% AM P. 226' Actua- RATING AM P RECEIVER I -.4 AND AMP- FILTER g g 5 lNVENTOR ALEXANDER MLEAN woman ATTORNEY Patented Apr. 16, 1940 unirso TATE-s TWO-WAY TELEVISION SYSTEM Alexander McLean Nicolson, New York, N. Y., asvsigner to Communication Patents, Inc., New

York, N. Y., a corporation of Delaware Application May '1, 1928, Serial No. 275, 72 v a 4 Claims. (01. 1786) This invention relates to a method and apparatus for facsimile transmission or television and more particularly to a method and apparatus for providing two-way televisionbetween two rel- 5 ative separated'stations, 'togetherwith telephone communication, if desired, either over wire lines 1 or through radio channels. a

It is; an object 'of this invention to provide a method and apparatus whereby the subject, at one'station, which I term the home station, is scanned, and a series of signals representing the image of the subject is transmitted to what I term the distant station fiwhile simultaneouslyat the distant station the image received from the home station is projected or exposed to the view of the subject at the distant, station, and

simultaneously the subject at the distant station is scanned and a series of signals transmitted from the distant station to the home station are projected as the image of the-subject at'the distant station in View of the subject at the home station. 1 Y h It is a further object of this invention to provide a method and apparatus by which as'ubject may be scanned, while simultaneously there is projected or exposed to his view an image of the subject at the distant station, without interference by the received image with transmission scanning. v 1

- It is a further object of this invention to provide a method and apparatus whereby the same source of illumination may be utilizedto produce an image of a distant'object in view of the home subject whose image is to be transmitted, and

simultaneously to scan the home subject.

It is a further object of this. inventionto provide a system of the class described in which the synchronizing at all of the stations is controlled by a master source of synchronizing cur- 40 rents at one station, and in which the receiving and transmitting scanning apparatus at any par ticular station is operated bya single prime mover synchronized withsaid master source of synchronizing currents. 4:5. It is a further object of this inventionto provide a system of the class described in which scanning elements at different stations maybe caused. to operate atthe same or synchronous speed, and to take and maintain the same relative 50 position with reference to the image, regardless of a difference in position at the beginning of operation, or at any time therein.

It is stilla iurther'object of this invention is provide such'a system in which any station may,

55 be set into operation and synchronized with the adjustments.

, scanning elements in the same relativeposition" 1 transmitter station may transmit both sounds and images to any desired number of receiving stations under the complete control of thetransmitting station, so that if any observer wishes to receive the broadcast matter, he may simply close a switch, and the receiver will be put into operation,- the receiving scanner synchronized with the. transmitting scanner, as'to speed of travel, and adjusted thereto as to space'l position on the 15 image, and this condition maintained indefinitely, under control of the transmitter and without requiring further attention from the observer.

, Still other objects and advantages of my invention will be apparent from the-specification. c 20 The features of novelty which I believe to be characteristic of my invention are 'set forth with v particularity in the appended claims. My invention itself, however, both as "to its fundamental principles and as to its particular embodiments 25;.. will best be understood by reference to the speciaccording to my invention, showing the focussing 30:

screen and lens removed from the transmitting scanning apparatus; I, 1 c

Figure 2 isa top plan vi ew of the apparatus shown, in Figure 1, with the focussing .screen in 1 place; 35'

. Figure 3 is a front elevation view of oneform of apparatus according to my. invention, in which one set of electrodes is utilized in both the trans mitting and receiving scanning apparatus; Figure 4 is,a top plan view of the apparatus shown in Figure 3; I I Figure 5 is a diagrammaticview of apparatus in which the same electrodes are used alternately for transmitting and receivingscanning; -1

Figure 6 is adiagrammatic view of'a complete station in] which reception and transmission is" carried on simultaneously, and in which the subject is scanned for transmission and simul-t taneously the received imageis-exposed tohis for transmitting signals controlling light intensity, speed and position of a receiving scanner;

Figure 10 is a circuit diagram of a receiver adapted for operation on signals received from apparatus such as shown in Figure 9;

Figure 11 is a circuit diagram of a receiver utilizing vacuum tubes for speed and position control;

Figure 12 is a circuit diagram of a slightly modified form of apparatus such as'shown in Figure 11; and I I Figure 13 is a circuit diagram of receiving apparatus utilizing the phenomenon of resonance for speed and position control.

It is known that in order to transmit images, a signal must be sent which successively indicates the light intensity at each elemental section of area of the image, and at the receiving apparatus a source of lightmust be controlled so that it corresponds not only in intensity but also in position to each particular element ofthe area of the image to be transmitted. Some form-of apparatus must be utilized at the transmitter whereby the light sensitive element, such as a photo electric cell, is successively subjected to light refiected from successive elements of the area of the subject, and simultaneously at the receiver similar apparatus must be used, which causes a light to play over a surface in the same pattern which is followed as-a'result of the functioning of the transmitting apparatus. This apparatus is termed the scanning apparatus, that used at the transmitter being designated as the transmitting scanning apparatus, and that at the re ceiver being designated as the receiving scanning apparatus.

The transmitting scanning apparatus is driven by a suitable prime mover, preferably a synchronous motor energized from currents of predetermined frequency, and the receiving scanning apparatus is driven by a similar prime mover energized by currents of the same frequency, which may be, and preferably are, transmitted to the receiving apparatus over the same or difierent channel from that used for the transmission of light controlling signals.

In order to make possible two-way television, it is necessary to provide at the home station and 'at the distant station orstations, apparatus by which the subject is scanned for transmission to the other stations, and also on apparatus for exposing in view of the subject the image reconstructed from the signals received from the otherstation. I I I I In accordance with my invention, I provide a single apparatus which I may term a duplex scanning apparatus which simultaneously scans thesubject whose image is to be transmitted and produces in view of the subject the'image received.

In its preferred form, the duplex scanning ap paratus, according to my invention, consists of apparatus arranged to scan the subject and to reconstruct the received image, driven from a single prime mover, such as a synchronous motor,- -which, in turn,is driven by a source of alters ating current of predetermined and fixed frequency.

In accordance with one form of the duplex scanning apparatus, there may be provided separate sources of illumination arranged side by side, and operating simultaneously and in synchronism.

In accordance with another form, I may utilize a single source of illumination, which opcrates-"successively at predetermined intervals to scan'the subject for transmission and to pro duce the received image.

In accordance with still another form ofmy' invention, I may utilize a single source of illumination which simultaneously scans the subject for transmission and produces the received image,

together with arrangements for preventing fluc- I tuations of illumination due to the received signal from appearing in the transmitted signal;

In all of these forms of apparatus, a single prime mover is utilized for driving the moving, parts of the apparatus in both the transmission as many stations as desiredmay be,utilized,-by' providing the appropriate apparatus: but in any case, 'I prefer to utilize a master source of synchronizingcurrent atone station, which con trolstl'ieprime movers in all'of the stations,-thus eliminating the necessity for transmitting syn-,

chronizing signals in both directions between the home station and the distant station, and preferably the apparatusin all "other stations is arranged as will hereinafter be described in detail so that all speed control at stations other than the master. station is operated by apparatus con-j trolled by the-master station, so that no manual adjustment is required at any station other than the master station, either in starting or maiIntaining operation.

In order to prevent the illumination of the subject, due to the received image, from aifecti'ng the transmission scanning, I prefer to scan the subject for transmission by means of radiant energy outside the range of visible light, preferably by infra-red radiation or ultra-violetv radiation;

and the photo electric cells or other apparatus for converting the radiation energy reflected back from the subject, into current or potential. variations, are preferably protected by a suitable energy filter to'prevent undesired response of the apparatus to visible light radiation. I Referring now more particularly to Figure 1, I have shown an intercept scanning apparatus of the type described and claimed in my copending application, entitled Scanning system for television, filed October 26, 1927, Serial Number 228,712, comprising a relatively movable electrode I adapted to sweep by a stationary electrode system 2, in close proximity thereto, but without making actual contact. ,The electrode I may be a knife edge -or wire provided with points, projec I i tions or serrations, and the stationary electrode 2 may comprise similar knife edges, Wires-or the like, provided with similar points or serrations,

and may be made up of a plurality of electrodes 7 5, B, I, 8, 9, m, H, I2 and I3 disposedadja'cent to each other and at a slight angle with respect to each other.

Theelectrodes 5, 6, 1 I 3, are mounted between support rods l4 and l5, and are preferably connected together and to one terminal of a suit able source of potential, the "other terminal of which is connected to the electrode I I. The source of potential may be an alternating current source, such as a vacuum tube oscillator or the like, of any desired frequency,zor a plurality of sources may be utilized of difierent frequencies, 75] I and in addition, if desired, there may be provided a source of direct current, as more particularly shown and described in the application above referredto. g j The electrode I may be mounted upon a carrier rod Ia and is preferably arranged to be moved at constant speed past the electrodes .5, '6 I3 in' a direction, for example, as shown by the arrow A. As the electrode I moves, a discharge is produced between it and the electrodes 5, 6 I3 successively, which discharge moves laterally across these electrodes, in the direction shown by the arrows B, at a relatively high rate of speed. If the sourceofpotential energizing the said electrodes is main' tained constant and the spacing of the electrodes properly chosen, and the magnitude andfrequency of the potentials properly chosen, the intensity of the discharge will be constant.

As pointed out in the applications herein referred to, the discharge may operate in the atmosphere, or one or both of the electrode may be enclosedwithin a chamber containing atmosphere or any suitable gas or mixture of gases,

' at a pressure greater or less than atmospheric pressure; and if desired, vaporizable substances, such as mercury, salts and the'like, may be en'- closed in the said chamber; gases, such as neon, at a pressure of a few millimeters of mercury, are found to be satisfactory.

Inthis instance, an'opaque screen 30 may be provided interposed between the electrode system I and 2 and the subject to be scanned. This screen may be provided with a small opening at its -center,-such "as a pin hole, or a larger opening may be provided fitted with a' lens 3| of any suitable type for the radiation employed. Suitable radiation responsive devices, such for example asphotoelectric cells 26 and 21 may be placed in such position as to receive the radiation reflected. back from the subject; and in caseit is desired to scan the subject'by infrared radiation or ultra-violet radiation, the light sensitive cells will'be protected by a filter such as 28 and 29 chosen, to pass, onlythe desired radiation to the cells. The output of the cells maybe amplified by suitable apparatus, such for example as a multi-stage vacuum tube amplifier system, to the-desired strength.

' If the carrier rod Ia be mounted upon a chain, as shown in the applicatlon above referred to, so as to pass successively across-the electrode system 2, and *if a series of similar electrodes I be mounted upon a chain at the proper interval, and if the correct number and spacing of the electrodes 5, 6,], be chosen in accordance with the size of the image which'it is desired to transmit and the amount of detail to be transmitted, then it will be understood that as the electrodes I pass across the electrode system 2, a discharge will be produced which successively illuminates all elemental areas of the image. Refiection--from these elemental areas to the photo electric cells, produces in the output of these cells an electro-mot'ive'iorce or current proportional 'to the lightintensity of the elemental areas of the subject, which electro-motive force or current may be utilizedto control a trans-mitter of any suitabletype.

If now, it beassumed that signals of a similar type are being received from the distant station, these incoming signals may be caused to reproduce the image at the distant station by impressing a potential corresponding thereto upon a similar electrode. system comprising movable electrode 3 and stationary electrode system 4 made up of cross electrodes I6, I'I, I8, I9, 20, 2|,

22, 23 and 24 mounted upon support bars or rods rod Ia, and operating in synchronism therewith. It will now be appa ent that if the sub-v ject stands in position to be scanned by a transmitting electrode system I and 2', he will observe the image produced by the receiving electrode systems 3 and 4; if the illumination produced by th receiving system is not sufiicient to affect the photo electric cells, it will not be necessary to utilize a difierent type of radia tion to scan the subject for transmission, and the lens 3| may be of the ordinary type, and the protective filters 28 and 29 may be omitted. If however, the illumination produced by the receiving screen is sufficient'to aifect the rewill be employed to protect thephoto electric cells C 28 and 29.

Referring now I more particularly I have shown an arrangement in which a single set of stationary electrodes 'is utilized both for transmission and reception scanning. In this instance, 40 designates an electrode similar to the electrode I, which may be utilized to produce the transmission scanning discharge, and

4| 2. similar electrode spaced therefrom, which may be utilizedto produce the rece'ivingscan ning discharge. The stationary electrode system 42 may be made up of a plurality of parallel knife edge or wire electrodes, -mounted upon carrier rods l4 and 25, and the electrodes 40 and 4| are mounted upon the frame so as to move together as in the case of the apparatus shown in Figure 1.

The source or sources of potential for producto Figure 3,

ing the transmitting scanning discharge are connected between the electrodes 49 and' lil. The source or sources of potential for producing the receiving scanning discharge are connected between the-electrodes II and 42, and it will be understood that as the electrodes" 41! and M move downward in the direction shown by the arrow A, they pass at an angle over'the stationary electrodes of the system 42, and a'series of discharges are produced travelling in the direction shown by the arrow B. It will be noted that in this instance, the electrodes 4.!) and M are shown-as mounted at a slight angle 'with respect to the electrodes of the system 42: the angle will preferably be so chosen that the trailing edge of the electrodes 40 and 4! passes off. one electrode at the instant the leading edge passes over the next screen 43 will not-interfere with the perception of the image produced by thereceiving.electrodes. The nature of the electrodes 40 and M and of the potentials supplied thereto will preferably be so chosen that the transmission discharge is relatively rich in radiation of the desired nature, and relatively'weak in visible radiation, in order to prevent loss of detail of the receivedv image.

Referring now more particularly to Figure 5, I have shown an arrangement in which the same electrodes are utilized alternately for transmis sion and reception scanning. In this instance, movable electrode 5 and stationary electrode system 46 may be arranged as shown in Figure; 1, and provided with a screen 43 as in- Figure 4. A

suitable commutator device 47 may be arranged to periodically connect the electrode 45' to the transmitting source of potential and to the receiving source of potential. For example, 52 and 53 mayde'signate respectively the receiving source of potential and the transmitting source of potential, the transmitting source of potential being constant and the receiving source of potential being controlled by the incoming signals. A

: rotating contact 48 may be provided, connected to electrode 45 and adapted to pass successively over segments 49 and 50, segment 49 being con-- nected to -one terminal of the transmitting source of potential 53 and the other terminal of which may be connected to ground or to a common return. The segment 50 is connected to one terminal of the receiving source of potential, the other terminal of which is connected to ground or a common return. The electrode system 46 is likewise connected to ground or to the common return. The rotating contact 48 may be driven through suitable connection with the prime mover M, which drives the scanning apparatus. The speed of operation of the commutator 47 may be so chosen that any part of one, or one, or more single images, is scanned for transmission and then for reception, but it will be understood that it is undesirable to scan for transmission or re ception for a period longer than of a second, as to do this, would cause the image to flicker.

Referring now more particularly to Figure 6, I have shown a system in which the same dis-. charge is utilized simultaneously for transmission and receiving scanning: in this case, 60 designates a movable electrode adapted to sweep at an angle over the stationary electrode system 6|. A screen 02, transparent to visible light but opaque to infra-red and ultra-violet, is provided having a pin hole or lens 63 transparent to infra-red or ultra-violet. The electrode 60 is connected to one terminal of the output of a filter 64, which is used in case the synchronizing currents are generated at the transmitting station, the other terminal of the filter being connected to the electrode system 6!. The filter 64 is in turn connected to the output of the amplifier 65, which is fed through transformer 61 from the receiving antenna 66. The filter serves to separate the synchronizing currents from the light controlling currents. The synchronizing currents derived from the filter may be passed through suitable amplifiers and utilized to operate the prime mover or driving motor, which moves the electrode 60. The light reflected from the subject is allowed to fall upon the photo electric cell 68, the output of which is amplified by a suitable amplifier 69.

It will be understood that fluctuation in the light intensity of the discharge will produce an undesired component, which represents the incoming signal, and the signal, as transmitted,

shouldbe free ofanySsuchfiuictuatiorf. For this purpose, a;portion of the voltage or current'sup plied to the electrodes may be utilized to eliminate e the undesired component from the output of the photo cells. The voltage drawn from the-output of the filter, 64 may be passed through a phase.

and intensity controller 10, which may comprise avacuum tube amplifier affording a variable am amplifier 69, in such a direction as to neutralize the undesired current fluctuations due to fluctuation of the illumination on the subject. The cancellation may be effected by means of coils ll and i2 suitably coupled. The output of the am:

plifier 69, after cancellation of the undesired component, is impressed on a suitable modulator l3 controlling the output-of suitable oscillator, which may be a vacuum tube oscillator of the type well known in the art, the output of which is impressed upon the transmitting antenna 15. It maybe pointed out inthis connection that to prevent oscillation of the entire system through reception upon antenna 660i signals transmitted from the antenna 75, it is desired to operatethe transmitter at a frequency sufficiently different from the receiver to permit of ready exclusion from the receiver of signals transmitted from the same station, and in addition geographical sep-,

aration ofthe transmitting-and receiving antennae may be employed, I

Referring now more particularly to Figures 7 and 8, these two figures show diagrammatically a complete two-way telephone-television system,

utilizinga home station anda distant station, v

Figure 7 being arbitrarily termed-thehome station and Figure 8 the distant station.

Referring now more particularlyto' Figure 7,

designates transmitting scanning apparatus,-

which may, and preferably will be, one of the arrangementsshowni-and described herein, but

it is to lie-understood, that insofar as the operation of thesystem is concerned, other forms of scanning apparatus may befutilized, as-for-ex-,

ample those shownanddescribed in my copend ing applications, entitledWScan-ning system for television, Serial Number-228,712, filed October 26, 1927, Method and apparatus for television and the like, Serial Number-218A25, filed September 9, 1927, High-[speed television system 5 Serial Number 222,417, filed September 28,. 1927,

and Pilot television system, Serial -Number 225,415, filed October 11, 1927, or any other suitable form ofscanning apparatus, such for exam ple, as those well known-in the art. The scanning apparatus is driven from a suitable primev mover 83-, which may, andv preferably will be, a synchronous motor operating on currents, for example having a frequency in excess of 2,000 cycles. i i-mechanical connection such ascoupled shafts 8| and 82 may beutilized for driving the scanningapparatus. The prime mover 83 may be energized by a source of alternating current,

such for example as alternator 93 generating cur rents of the proper frequency, A photoelectric cell or cellsare provided as at 84 adapted to receive the radiation reflected from thesubject,

and the output of the photoelectric cells is amplified by a suitable amplifier 85, which may comprise the necessary number of stages of thermionic amplifiers. The output of the amplifier'85 is supplied to a modulator 860i any suitable type known in-the art, which serves to modulate the output of the oscillator :87, likewise of any suitable type known in the art.

The output of the oscillator 81 may be amplified if not of 'thedesired intensity, or if of suiiiicient intensity, may be applied directly to the transmitting antenna 88 or to a carrier circuit leading to the distant station. The output of the source of synchronizing currents 93, which I may term a master source,'is also supplied to the modulator 06, and may beimpressed upon the transmission frequencyoscillations as a separate tone modulation. In addition, there may be provided'a'microphone 89 of any suitable type, as for example, the well-known carbon button type, energized bya local battery 90,and coupled through transformer 9I to a suitable amplifier 92. The output of the amplifier 92 may be supplied to modulator 86 and for the purpose of modulating the output of the modulator 8'! in accordance withspeech.

In case the frequency of the currents to be transmitted interferes with the transmission of the synchronizing currents, the synchronizing frequency may be raised to a point where such interference is overcome, or as an alternative, the amplified microphone currents may be utilized to modulate a second oscillator, of a frequency outside the range of speed frequency, and this modulated oscillation may itself be impressed upon the transmitted oscillations as a modulation.

It will now be seen that 'as the subject is scanned for transmission, signals representing his image will be transmitted from the antenna 88, and if the subject speaks, his voice will be picked up by the microphone and similarly transmitted. The transmitted signals are. received at the distant apparatus upon the antenna I02 and impressed upon amplifier I03, where they are amplified to the extent desired. The amplified currents are then passed through a suitable filter I04, which serves to separate the currents of the various channels: for example, the amplifier I01 may receive the synchronizing currents which are amplified to the extent desiredand passed on to synchronous motor I08, whichis preferably similar to the synchronous motor 83, and operates at the same speed on currents of the same frequency. I

The motor I08 comprises a'suitable shaft I09, which serves'to operate the transmitting-scanning apparatus IIO; Photoelectric cell or cells I20 are provided upon which the reflected radiation from the subject at the distant station falls. The output of the photoelectric cell is impressed upon the amplifier the extent desired, after which it is supplied to modulator I-IS serving to modulate the output of oscillator H9, which energizes the transmitting antenna I22.

In this connection, itshould be noted that the frequency of the oscillator IlQshould be chosen sufficiently far, removed from that of oscillator 01, so that ready separation of the two frequencies may be obtained. The incoming signals at the distant apparatus, corresponding to speech frequency, are separated by thefilter I04 and supplied to the detector Ina-after detection, the speech currents are amplified to the extent desired by the amplifier I I3, and impressed upon the loud speaker H4. 1 The light controlling signals are separated by the filter and impressed upon the amplifier*I05, the output of which is supplied to the receiving scanning apparatus I06, which may be, and preferably will be, ofthe-type I2I, and there amplified to herein shown, or may be any of the arrangements shown and described in my copending applications above referred to, or alternatively, any of the well known types of scanning apparatus.

At the home station, the signals transmitted from'the antenna I22, are received upon antenna 9d and impressed upon amplifier 95,where they are amplified to the extent desired. The output of the amplifier 95 may be supplied to the filter 96, which serves to separate the speech currents and the light control currents. The speech currents are transmitted to the detector 91, thence to the amplifier 98 and thence to the loud speaker or similar receiver 99. The light control currents are impressed upon the receiving scanning apparatus Illt, and driven from the prime mover 83; by means of shaft IIiI coupled to shaft 82.

In this connection, it should be noted, that the transmission of synchronizing currents takes place only from the home station to the distant station, and not from the distant station to the home station. It will be clear that the transmission-of synchronizing currents from the distant station to the home station is not necessary, since in the home station the transmitting and receiving scanning apparatus is driven in synchronism by the motor 83 operating from master synchro'- nizing source 93. In the distant station, the

mover 83: and the prime mover I08 drives the receiving and transmission scanning apparatus at the distant station, from which it will be seen that merely by the transmission of synchronizing currents from the home station to the distant station, all four scanners are operated in synchronism. However, it will be understood that in case it is desired, the synchronizing currents received at the distant apparatus, may be transmitted back to the home station for the purpose of comparison or regulation, but this is not essential.

While I have shown and described byway of example, a single home station and a single distant station, it is to be understood that several distant stations may be provided and that a specific frequency band may be selected for transmission in each direction between the various stations. For example, if we indicate the home station as A and the distant stations 13,0, and D, one band of frequencies may be selected for transmission from A- to B and a second band for transmission from B to A: similarly, a third band may be selectedfor transmission from A to C, and a fourth band from C to A, a fifth band from A to D, anda sixth band from D to A: also, in the event that broadcasting is desired, the station A may transmit always on the same frequency, and the various distant stations may be tuned to receive that frequency. In the foregoing, the method of and apparatus for synchronizing the operating stationshas been described only in a general way to establish its relation to theremainder of the system. The particular arrangement and operation of apparatus for exactly synchronizing the various. stations will now be described'in more detail,

In order for such a system'as is here discussed to be capable of wide and effective use, the apparatus should require no greater: intelligence and skill on the part of the operator than can be exercised by the average person, as clearlyit is impractical to require a highly skilled operator I these signals are received at times when the reat every station, as for instance at every receiver in a television broadcasting system.

The operation of a receiver controlled in speed by a distant transmitter presents two principal difiiculties. First, there is the difficulty of maintaining exactly the same speed at both stations, and secondly, there is the difficulty of bringing the scanning apparatus mechanically in step at both stations as well. This latter difficulty may result in parts of the received image being displaced with respect to the other parts. For example, if the scanning apparatus is operating at exactly the same speed at the transmitting station and at the receiving station, and if the receiving scanner is half way across the screen at the instant the transmitting scanner is operating on the beginning of the image, it will be apparent that at the receiver, the image will be cut in half and the two halves transposed in position.

It is clear that since there is only one space position of the receiving scanning apparatus relative to the transmitting scanning apparatus which will be correct, when synchrony is estab-.

lished, and there are many possible positions which will be incorrect, some means should be provided which will not only cause the receiving apparatus to come to synchronous speed, but which will also cause the receiving scanning apparatus to run faster or slower than the transmitting scanning apparatus, until it occupies the same position relatively to the image, and when. this identity of relative position is attained, syn-' chronous. speed is to be maintained: and furthermore, should the receiver and transmitter get out of step, they must be brought back in step, and the receiver again brought to synchronous speed.

The images at transmitter and receiver may be considered as fixed within what I term a frame of reference, and each comprises a large number of picture elements scanned in a unit of time and in a predetermined pattern or sequence, each frame being repeatedly scanned at the rate of 16 to 18 frames per second. If the scanners at the receiver and transmitter are operating at the same speed and pass corresponding points in the frame of reference at the same time, the received image will at all times be properly placed in its frame of reference or framed.

Therefore, if the master or transmitter station sends a signal periodically and repeatedly whenever the transmitting scanner passes a predetermined point of reference, this signal may be used to bring the receiving scanner into step, and it follows that if this signal be repeated with sufficient rapidity, the receiver will be kept in step at all times during operation.

of maintaining synchronous speed of the driving motor and space position of the scanner.

To this end I provide apparatus for transmitting periodic impulses or signals of some sort at definite time intervals representing definite space positions of the transmitting scanner, and I provide at the receiver apparatus such that if ceiving'scanner is in an incorrect position, then thereceiving scanner is caused to accelerate or retard as the case may be, until the space position of the receiving scanner is correct at the instant of receipt of such signals; when this condition is reached, the accelerating or retarding force is rendered inoperative or ineffective, as

long as the desired condition obtains.

Referring now more particularly to Figure 9,

In other words, such a signal may serve the double purpose I30 designates. diagrammatically. a generator driven by any suitable prime mover, and generating currents of the, desired frequency for operating motor I3l, which in turn operates scanning apparatus ,of any suitable type, such as herein shown and described, or any other form of scanner known in the art. The apparatus for sending a signal at predetermined recurrent points, representing definite space positions of the scanner, I terma metronome, and the sigsignal. The metronome comprises a suitable source of high frequency currents, such as a vacuum tube oscillator I31, from one terminalof which a connection passes to coil I 38, thence to the shaft I32, which drives the scanning apparatus. Mounted on shaft I32 I provide a suitable device for periodically closing a circuit through source I31 and coil I38. Inthe form shown, this may comprise conducting disk I33 provided on its periphery with a coating of insulating material except at point I35. Engaging the periphery of disk I33, I may provide a contact finger or brush I36. f

It will be seen that in the operation of this arrangement, coil 138 is momentarily traversed by high frequency oscillations atthe instant that conducting point I35 passes under contact I36, and this may be arranged to take place at the instant that the scanning apparatus, driven from the shaft I32, is operating on the first element of the image.

In the particular arrangement shown, therecoil I38 every time the scanning apparatus passes through initial position with reference to the image. It will be understood, however, that the contact may be closed to permit oscillations to pass through coil I38 with greater or less frequency, by the interposition of suitable gearing for driving the disk I33, or by other arrangements, as will be understood. A second coil I39 is provided, which may be shunted across the power line connecting the generator I30 and motor I3I: and a third coil M0 is provided, inwhich currents are flowing from the outputof'the photo cell amplifierri Thecoils I38, I39 and I40, are all coupled to coil I4I, which feeds a suitable modulator andosclllator I42, diagrammatically shown, in such manner that the carrier frequency transmitted is modulated by the currents flow- ,ing in coils I38, I39 and l iil.

The arrangement of said coils, modulator and I oscillator, isshown only in diagram, as this ar-.

rangement per .se forms no part of my invention, and is well known inthe art, The modunal transmitted therebyl term the metronome fore, high frequency oscillations will pass through lated carrier frequency oscillations are passed through coil I 43, and thence to coil I46 inductively coupled thereto, which isconnected in circuit with antenna I44, and if desired, a tuning condenser I41 may be associated therewith. It will be understood thatall' of the modulating currents may beamplified, if desired, to a greater or less extent, and that in case it is desired, one or more of these modulated currents may be impressed as modulations upon separate carrier 1 frequency oscillations which in turn may be used to modulate thecarrier frequency of the station. Since the particular'apparatus for modulating carrier oscillations, which modulated oscillations are in turn used to modulate another carrier, is well known in the art, it is not described in detail.

It will be understood that the signal radiated aieaoos from the antenna 444 comprises three-compm nents: (l) the component indicating thevalue .of' light intensity at a particular time at the transmitter; (2) the currents representing the frequency of, the motor generator system I and I3I; and, (3 signals representing thepassage of the transmitting scanning apparatus over a particulargpoint of the frame of reference, and while I'have indicated a method and apparatus for transmitting. all of these signals of a similar carrier wave, it will be apparent that difficulties of'modulation [andseparation may be avoided if desired, by transmittingeach of these ceiving apparatus, 'which I term' a synchronome, adapted to operate in response to signalstransmitted from a system-operating as just de scribed. In this arrangement, I50 represents an antenna provided with inductance I5I, shunted if desired, by a tuningcondenser I52: .the in- 'ductance I5I is suitably coupled to a. second inductance I53, which feeds .the input. circuit of a suitable receiver and filter 154, which may comprise as many stages of radio frequency am-' plification as desired, together with detection and the necessary filtering circuits separating the [:various signal components from each other and from the received carrier.

The photo cell currents arepassed to-the light control apparatus, as shown diagrammatically by leads disignated to light control, and it will be understood that these currents maybe amplified to the extent desired. The currents representing the frequency of motor-generator systern I36 and I3I, may be amplified by suitable ergized by the incoming metronome signals,

amplifier I56, and may beconverted, if desired, by means of. a converter I5'I, to currents of the phase desired. In thearrangement shown, I have illustrated the output of converter I51 as being supplied to a suitable threephase. motor I585 in this connection, it is desired to point out thatpreferably motor I3I and motor I58 should havea's near as possible, the same operating characteristics, so that these two motors, under normal conditions, will operate at substantially the'samespeed. M0unted. on the rotor of motor I 58, I may provide a series of coils I64, herein diagrammatically shown for purposes of simplicity, as a. single coil, preferably mounted on a pivot I64A at one end so as to be free to align themselves radially under the action of centrifugal force when the motor is operating at substantially synchronous speed.

I also provide a series of stationary coils I65, adapted to co-act with coils I64 and connected in series therewith through a circuit comprising contact I651 bearing on slip ring I59 of the shaft I5 8aof motor I58; and also'by means of contact I62 bearing on slip ring I6I insulated from the shaft of motor I58.

The coils I64 and I65'are arranged-to be en- 7 vide an insulating segment I63 on the periphery of the disk or slip ring I6I, so that the-circuit through coils I 64' and I65 is periodically interrupted at one point during the revolution of slip ring I6I: at all other times, the output circuit of amplifier I55 passesthrough coil I65 to conta'ct I thence to slip ring I 59, thence through speeds It will be noted thatI procoil I64 to slip ring I6I to contact I62, and thence through a suitable tuning condenser I66 to amplifier I55.

The coils I64 should be arranged so that at substantially lessv than speeds, the coils I64 will not be extended radially outward, and will have verylittle effect: however, as the motor I58 reaches'synchronous speed,

these coils will swing into position with their axes extending radially in position to co-act with stationary coil I: the insulating section I63 is so positioned on the slip ring I6I, that it interrupts the output circuit of amplifier I55 when the position of the receiving scanning apparatus operated by motor I58 corresponds to the position desired: that is to say, in case theutransmitter sends out a metronome signal at the instant, the scanning apparatus passes across the synchronous first element of the image, then the insulating I segment I63 will be so positioned with respect to the scanning apparatus driven by motor I58, that insulating segment I63 passes under the contact I62 at the instant that the receiving scanning apparatus driven by the motor I58,

. passes across the first element of the receiving screen.

f it be assumed that the motor I58 is operating at the same speed as the ,motor I3I and the instantaneous positionoi the transmitting and receiving scanning apparatus with respect to be, it being understood that the polarity of all of the coils is so chosen as to obtain maximum action. 7

For the purpose of discussion, it may be assumed that the coils'are so wound, that upon the, passage of current therethrough, they are attracted. It will then be apparent that if the motor I58 is operated at less than synchronous speed or is out of proper position with respect to the frame of reference, then every time a metronome signal isreceived, an impulse will be delivered to the motor I56 tending to speed. it up,'provided the space relation of the coiis I64 and. I65 is properly chosen. On the other hand, if the motor I56 is operating at greater than synchronous speed, it is apparent that the position of the coil I64 will be such that it will be retarded by the action of the currents COI'I'Q?" spending to the received metronome signal.

In order to prevent a condition of more or less continuous hunting by the motor I58, it may be desirable to arrange the said motor so that it willnormally operate at a speed relatively a little slower than synchronous speed, so that correcting or accelerating impulses are supplied thereto periodically, so as to maintain synchronous speed. I

It will also be observed that withsuchan arrangement, regardless of the space position of the receiving scanner with respect to the frame of reference, the driving motor cannot operate at synchronous speed until the correct position with respect to the frameof reference has-been reached, and this makes it possible to provide a :sing1e'masterswitch, operable for example by'V75' remote control, if desired, which master switch may bearranged to close all the necessary circuits to set the receiving apparatus in operation.

Therefore, it becomes possible to operate a television broadcasting system, requiring no skill on the part of the operator at the various receiving stations, since if the transmitting station is in operation and it is desired to receive from it, the receiving operator need only push a single start-stop switch to starting position, whereupon the receiving apparatus will be set into operation,

as already described, and will continue tofunction under the complete control of the transmitting station as longas the master switch is kept closed, no attention being required on the partof the receiving operator.

Referring now more particularly to Figure I have shown diagrammatically another form of synchronome or synchronous receiver for exactly keeping step with the master metronome at the transmitting station. In this arrangement, :I have shown the same receiving antenna and frequency filter as indicated in Figure 10, but utilizing thermionic vacuum tubes as controlling devices to difierentiate between periodically generated master and local signals.

The received metronome signal, picked'up by the coil I15, is applied to the control electrode I19 of the thermionic tube I18. This signal is amplified sufficiently to energize the coil I 8|, controlling the speed of the synchronome motor I83. It will be observed that the tube is provided with the usual cathode I11 and anode I18, which is energized by the battery I 82, and the input circuit may include a tuning condenser I88. When the output coil IN is energized, part of the amplified signal is transferred to the coil I93 to control or block the activity of a similar thermionic tube I88, having a cathode I81, anode I88 and control electrode I89. The current induced in the coil I93 may be rectified by rectifier I92 of any suitable type. The rectifier when it is energized, passes negative charges, corresponding to the rectified metronome signal, to the control electrode I89 of the thermionic tube I88. This vacuum tube amplifier normally is energized by a local signal, similar to the master metronome signal generated by oscillator I98 and supplied periodically by a contact device I98 attached to the shaft I95 of the synchronome motor. The local or synchronome signal may be produced by a high frequency generator I98, coupled to the synchronome motor I83, whence the spring I91 feeds the local signal, which passes through filter 298 to the amplifier I88 and through the coils I94 and I98; and a tuning condenser I9I may be provided to strengthen the input signals which pass the filter.

Both metronome and synchronome signals should comprise, near synchrony, high frequency oscillations of, preferably, similar periodicity.

7 When the output coil I85 is energized, a portion of the energy is carried by the associated coil I99 and is rectified by the rectifier I84 so as to pass negative blocking charges to the amplifier I88 from generator I98. The coils NH and I85 operate to accelerate or retard the synchronome motor I83, except that atspeeds much below synchrony, the accelerating coil I8I alone functions. cause the generator to pass energy of approximately speed frequency through thefilter, then the retarding coil I85, will be able to function in arresting the speedof the synchronome motor.

When the motor speeds up sufiiciently to Which coil operates to control the motor, depends on the advent of distant or local signal. When the metronome signal energizes the ampli- I86, and consequently suppresses energy flowin the coil I85. When the synchronome signal energizes the amplifier I86, it establishes a negativeblocking potential on the control electrode I19 of the amplifier 6, andlikewise suppresses energy flow in the coil I8I.

Accordingly, if the synchronome is running below metronome speed, it is accelerated, and if above it is retarded; in fact, it is maintained at synchrony. The currents in coils I8I and I85 are? amplified sufficiently to produce theenergy re-' quired to control the motor I83." If the frequency of the currents is low, as for example representingithe direct current fluctuations of the tubes I18 and I86, then ordinary field coils with mag-"- netic material for reinforcement of the flux may be used. On the other hand, high frequency curling system described in Figure 11; I show here a polyphase motor synchronome 208 driven synchronously with and by the master metronome I38 described in Figure 9. The received I54 filters and amplifies and supplies to output coil 202 the synchronome signals, described in Figure 11, and to coil 204 the polyphase currents necessary to energize the network system 281 and motor 298- of the synchronome.

. fier I16, it establishesa negative blocking potential on the control electrode I89 of the amplifier 40. If the speed developed by the motor 208 is approximately synchronous with the transmittingsystem I30, I3I, and the timephase sufiicient to cover a complete scanning element or reference frame as described, then the speed controlling coils I8I and I85 will take care of speed variations within the time and space represented by a single phasing of the motor system. Of course, the speed controlling coil may, at lower speeds than synchrony, have its action cut out by causing, as in Figure 11, the

synchronome motor 288 to drive the generator I98 and to suppress its oscillating currents by filter until the correct frequency is generated and passed to the coil I85, as aforesaid.

On the other hand, the local signal generator I98 may, as shown in Figure 12, be a self-sustaining oscillator whose energy is periodically tapped and transmitted, as indicated, to the retarding coil I85. 7 The rectifiers I84 or.I92, if of the gaseous tube type, may be shuntedwith suitable impedances 209 and 2H1, in order to maintain at high frequency rectifications, the tubes I16 and-I86 sufficiently discharged at .the conclusion of the master or local time signals, so as not to blockand interfere with the desired operation.

In Figure 13, I show a modified synchronome"- for attuning by the principle of resonance the' local apparatus to the incoming master metro nome signals. The receiver 22I delivers coarse .and fine synchronizing signals to coils H9 and 228 respectively, for driving and controlling the synchronome motor 2 I1. By means .of shaft 235,:-.75

the motor drives the wheel 232, which carries peripherally the suspended metallic plate 229 pivoted at 233. This plate is designed near synchronous speed, to engage capacitively corresponding conducting sectorsorv areas 230 and 23!, whose separation apart and distance from the fly plate 229 isadjustable. I

The condensive couples 229 and 230, and 229 and 23L when in conjunction near synchronous speed with the master metronome, energize one or other of the two resonant circuits 226 and 221, provided the metronome signal is being sent and received through coil 22E], amplifier 222 and the linesI2-28 and 234.

The mode of operation of the resonance synchronizer is as follows: the synchronome 2|! is driven from the receiver 2H3 at approximate synchrony, at which, also, the movable condenser plate 228 will fly out sufficiently far, centrifugally, to close, electrostatically, one or other of the resonant circuits containing respectively coils 22Band22l. I

For example, if the plates 229 and 230 meet in capacitative conjunction, then high frequency current from amplifier 222 will pass through the momentarily established electric condenser, thus formed, and will energize the coil 221 and amplifier 225: and coil or coils 2l6 will be strongly energized and may, for example, thus accelerate the speed of the motor 2H. Similarly, the coil or coils 215 may retard themotor when the capacitative currents'flow through the moving condenser system 229 and 23L Now, when the metronome signal occurs during conjunction of the plates, the synchronome is'either expedited or retarded, and at synchrony of the synchronome the fly plate will be passing just between the plates 23!) and 23!.

In order to assist rapidacceleration of the synchronome motor 2 H, the condenser plate 230 taking part in the process may have its functioning area tail off as shown in dotted lines at 236.

Inhigh' speed television and synchronization,

the wheel 232 should be geared to relatively highspeed with the shaft 235 of the motor 2": the separation between plates 230 and 23l and the width of the fly plate 229 should be reduced to a minimum compatible with sharp tuning.

While I have shown and described certain preferred embodiments of my invention, modifications and changes may be made without departing from the spirit and scope of my invention as will be understood by those skilled in the art.

I claim:

l. A two-way television system for simultaneous television reception and scanning comprising a home and a distant station each including an extended'fixed electrode, a movable electrode which signals for scanning a subject at the distant station, means controlled by said signals for varying the current supplied to the electrodes to vary the intensity of the arc, means for transmitting to the home station signals representing the subject at the distant station, and means at the home station controlled by signals transmitted from the distant station for varying the current supplied to the electrodes to vary the intensity of the arc and reproduce the image of the subject at the distant station.

2. A simultaneous two-way television transmission and reception system comprising a home and a'distant station, an extended fixed electrode forming a portion of a two dimensional'surface and a'movable electrode at each station, means for supplying electrical energy to said electrodes to create an arc between said fixed and moving electrodes,means for moving said movable electrodes rapidly and in synchronism to cause the arc totravel'over the fixed electrode and to create, visually, ateach station, a two dimensional illuminated surface and means at each of the stations for controlling the electrical energy supplied to said electrodes at the other station to vary the intensity of the arcs.

3. A simultaneous two-way television transmission and reception system comprising a home and a distant station, an extended fixed electrode over the fixed electrode and create visually at each station a two dimensional illuminated surface and means at each station responsive to the light cast by said are and reflected from a subject to be transmitted to the other station for controlling the electrical energy supplied to theelectrodes at said other station and thereby vary the intensity of the arc at said other station.

4. The television system set forth inthe preceding claim, comprising means for varying the amount of electrical energy supplied to the electrodes to compensate for variations in'illumination of the subject due to production of an image on said two dimensional surface.

ALEXANDER McLEAN NICOLSON. 

